The present invention relates to a photographic film cassette, and more particularly to an improved photographic film cassette in which the rotation of a spool therein having a photographic film attached thereto causes a leader of the film to be advanced externally of a cassette shell.
A conventional film cassette has photographic film positioned therein such that the film leader does not protrude from the cassette shell prior to loading the film cassette in a camera. Such a film cassette is easily loaded into the camera. Simple film-advancing mechanisms of the camera are used with the film cassette and have a construction which rotates the spool to unwind the film, thereby causing the film leader to move through a film passageway and exit from the film cassette.
One conventional film cassette, disclosed in U.S. Pat. No. 4,834,306, has a spool provided with flanges or disks on both lateral sides of a photographic film roll such that circumferential lips are formed on the periphery of the disks to project in a direction along the length of the film cassette. Spreading projections or guide projections are formed on an inside surface of the cassette shell in a film entranceway where the film is directed to a film passage mouth, and deform the disks outwardly to widen the interval therebetween. The guide projections also are formed as separating claws which separate the film leader from the outermost turns of the photographic film roll to direct the film leader to the film passage mouth. The guide projections continuously spread the disks in the film entranceway to disengage the outermost turn of the roll from the circumferential lips. Therefore, the film leader is advanced to exit the cassette shell through the film passage mouth by rotating the spool in a direction to unwind the film.
However, the film cassette described above has a disadvantage in that the spool rotation cannot be transmitted to the outermost turn of the film when the guide projections are formed in the film passageway entrance, because the film roll is loosened erroneously in a position under the film entrance. Thus, the film leader fails to advance through the film passage mouth even though the spool is unwound.
Another problem is that the film leader may be prevented from advancing by the guide projections contacting the film, since the guide projections contact the top of the circumferential lips of the disks to release the outermost turn of the film roll from the circumferential lips.